An electronic circuit has been recently higher in density, and the need for a smaller area and connecting resistance has been intensified regarding a packaged device. One of means for attaining a high-density package is flip chip package. Several kinds of packaging methods are available for the flip chip package, and in consideration of easy repair and unleading, which has attracted attention in recent years, SBB method (Stud Bump Bonding) is a desirable technique. The SBB method is a technique for forming protruding electrodes, which are made of materials such as Au, on a semiconductor element by a wire bonding method and for connecting the protruding electrodes and electrodes on a circuit board via conductive resin.
Referring to FIG. 3, a paste electrode material is firstly printed on a circuit board 11 by a method such as screen printing, and the circuit board 11 is baked at a temperature of sintering the electrode material. Thus, circuit electrodes 12 are formed on the circuit board 11. On the other hand, protruding electrodes 14 are formed on a semiconductor element 13 by a method such as wire bonding, and a layer of conductive resin 15 is formed on the protruding electrodes 14 by transferring and so on. Thereafter, the circuit board 11 and the semiconductor element 13 are positioned high accurately and a suitable load is applied thereon. Hence, the semiconductor element 13 is packaged on the circuit board 11.
However, the above conventional packaging method is disadvantageous as in the following. First, since the semiconductor element 13 has decreased in electrode pitch in recent years, an electrode pitch on the circuit board 11 needs to be smaller accordingly. However, according to the conventional screen printing method, a pitch is limited up to 300 μm and printing is difficult with a pitch below the limit, causing frequent short circuits and breaks in a wire. Consequently, the yields are lowered.
Secondly, when the semiconductor element 13 is smaller in electrode pitch, it is quite difficult to control a quantity of the conductive resin 15 transferred onto the protruding electrodes 14 of the semiconductor element 13. Particularly, short circuits are more likely to occur. In order to prevent the short circuits, a quantity of the conductive resin 15 is set smaller than that of the conventional art. However, since the electrode material expands laterally, the circuit electrodes 12 are each half-round in cross section when an electrode pitch is 100 μm. In the case where flip-chip packaging is carried out on the circuit electrodes 12, the conductive resin 15 is squeezed out of the circuit electrodes 12 as shown in FIG. 3. Therefore, the conductive resin 15, which is squeezed out of the adjacent circuit electrodes 12, may be short-circuited.